fp_rnd.h

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/*************************************************************************/
#ifndef FP_RND_H
#define FP_RND_H
#ifdef __cplusplus
extern "C" {
#endif
 
/*!***************************************************************************
 * @addtogroup  argus_fp
 * @{
 *****************************************************************************/
 
#include "fp_def.h"
#include <assert.h>
 
/*!***************************************************************************
 * @brief   Converting with rounding from UQx.n1 to UQx.n2.
 * @details Equivalent to dividing by 2^n with correct rounding to unsigned
 *          integer values.
 * @param   Q The number in (U)Qx.n1 fixed point format to be rounded.
 * @param   n The number of bits to be rounded,
 *              e.g. UQ8.8 -> UQ12.4 => n = 8 - 4 = 4.
 * @return  The rounded value in (U)Qx.n2 format.
 *****************************************************************************/
inline uint32_t fp_rndu(uint32_t Q, uint_fast8_t n)
{
    if (n == 0) return Q;
    else if (n > 32U) return 0;
 
    // Shift by n>=32 yields undefined behavior! Thus, this extra first
    // step is essential to prevent issues.
    Q >>= n - 1;
    return (Q >> 1) + (Q & 1U);
}
 
/*!***************************************************************************
 * @brief   Converting with rounding from Qx.n1 to Qx.n2.
 * @details Equivalent to dividing by 2^n with correct rounding to integer
 *          values.
 * @param   Q The number in (U)Qx.n1 fixed point format to be rounded.
 * @param   n The number of bits to be rounded,
 *              e.g. Q7.8 -> Q11.4 => n = 8 - 4 = 4.
 * @return  The rounded value in (U)Qx.n2 format.
 *****************************************************************************/
inline int32_t fp_rnds(int32_t Q, uint_fast8_t n)
{
    return (Q < 0) ? -(int32_t)fp_rndu((uint32_t)(-Q), n) : (int32_t)fp_rndu((uint32_t)Q, n);
}
 
/*!***************************************************************************
 * @brief   Converting with truncation from UQx.n1 to UQx.n2.
 * @details Equivalent to dividing by 2^n with truncating (throw away) the
 *          fractional part, resulting in an unsigned integer/fixed-point value.
 * @param   Q The number in (U)Qx.n1 fixed point format to be truncated.
 * @param   n The number of bits to be truncated,
 *              e.g. UQ8.8 -> UQ12.4 => n = 8 - 4 = 4.
 * @return  The truncated value in (U)Qx.n2 format.
 *****************************************************************************/
inline uint32_t fp_truncu(uint32_t Q, uint_fast8_t n)
{
    return (n < 32U) ? (Q >> n) : 0;
}
 
/*!***************************************************************************
 * @brief   Converting with truncation from Qx.n1 to Qx.n2.
 * @details Equivalent to dividing by 2^n with truncating (throw away) the
 *          fractional part, resulting in a signed integer/fixed-point value.
 * @param   Q The number in (U)Qx.n1 fixed point format to be truncated.
 * @param   n The number of bits to be truncated,
 *              e.g. Q7.8 -> Q11.4 => n = 8 - 4 = 4.
 * @return  The truncated value in (U)Qx.n2 format.
 *****************************************************************************/
inline int32_t fp_truncs(int32_t Q, uint_fast8_t n)
{
    return (Q < 0) ? -(int32_t)fp_truncu((uint32_t)(-Q), n) : (int32_t)fp_truncu((uint32_t)Q, n);
}
 
#ifdef __cplusplus
} // extern "C"
#endif
#endif /* FP_RND_H */